On Mon, Dec 10, 2012 at 02:05:09AM -0500, Greg Smith wrote:
> On 11/14/12 2:11 AM, Toby Corkindale wrote:
> >So on the face of it, I think the Sandforce-based drives are probably a
> >winner here, so I should look at the Intel 520s for evaluation, and
> >whatever the enterprise equivalent are for production.
>
> As far as I know the 520 series drives fail the requirements
> outlined at http://wiki.postgresql.org/wiki/Reliable_Writes and you
> can expect occasional data corruption after a crash when using them.
> As such, any performance results you get back are fake. You can't
> trust the same results will come back from their drives that do
> handle writes correctly. I'm not aware of any SSD with one of these
> compressing Sandforce controller that's on the market right now that
> does this correctly; they're all broken for database use. The quick
> rule of thumb is that if the manufacturer doesn't brag about the
> capacitors on the drive, it doesn't have any and isn't reliable for
> PostgreSQL.
>
> The safe Intel SSD models state very clearly in the specifications
> how they write data in case of a crash. The data sheet for the 320
> series drives for example says "To reduce potential data loss, the
> Intel® SSD 320 Series also detects and protects from unexpected
> system power loss by saving all cached data in the process of being
> written before shutting down". The other model I've deployed and
> know is safe are the 710 series models, which are the same basic
> drive but with different quality flash and tuning for longevity.
> See http://blog.2ndquadrant.com/intel_ssds_lifetime_and_the_32/ for
> details. The 710 series drives are quite a bit more expensive than
> Intel's other models.
It looks like the newer Intel 330 SSD also lacks a capacitor.
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ It's impossible for everything to be true. +
